Stuttering is a disorder of speech with a prevalence estimated to be 1% of the world's population. It is often a significant communicative problem for the individual, limiting educational and employment opportunities and social and psychological adjustment. The etiology of stuttering is unknown, and treatment strategies and outcomes are highly variable. A major impediment to understanding the etiology of stuttering and to the development of successful therapeutic techniques is the lack of understanding of the physiological bases of the disorder. Stuttering manifests itself as a breakdown in speech motor processes. The complex factors known to affect the occurrence of stuttering must ultimately have an effect on the physiological events necessary for the production of speech. There has been significant progress in understanding the physiological bases of stuttering in adults. Stuttering, however, is a developmental disorder with an average age of onset of 3-years. There is almost no work on the physiology of stuttering in young children to help us understand the etiology of the disorder. In our theoretical framework on stuttering, we posit that motor, linguistic, cognitive, psychosocial, and genetic factors play a role in the onset and development of stuttering. Further it seems likely that the influence of these factors changes over the lifespan of the individual who stutters. We elect to focus this project primarily on motor and linguistic factors and their potential interactions in preschool children who are stuttering and their normally fluent peers. We hypothesize that stuttering emerges when a child fails to acquire stable motor control and coordination processes for speech, thus making him or her vulnerable to breakdown in the face of increased processing demands. We test the hypothesis that children who stutter lag their normally fluent peers in developing speech motor control and coordination processes. Furthermore, we assess whether the speech motor systems of children who stutter are exceptionally sensitive to increased linguistic processing demands. We seek to determine if language processing differences detected in the brain activity of adults who stutter are also evident in the early years of stuttering. By employing a longitudinal experimental design, we can determine whether a set of physiological measures related to language and motor functions can discriminate children who will persist in stuttering from those who will recover. [unreadable] [unreadable]